Potential Assessment On The Carboniferous-permian Shale Gas Resource In Central Hunan

The reservoir-forming conditions and exploration potential of shale gas in Lower Carboniferous Ceshui Formation, Upper Permian Longtan Formation and Dalong Formation, central Hunan, were investigated on the basis of the data collection and collation, geological field work and indoor analysis. The follwing signicant findings have been obtained.The thickness of Carboniferous-Permian mudshale in central Hunan is large, with the highest level being about 200 meters in the center position of the depression. The total organic carbon contents of mudshale in the Carboniferous-Permian are high, with the average value being more than 2.5 percent. For the Upper Permian Longtan Formation, total organic carbon contents can be higher than 4 percent. The type of organic matter in mudshale are dominated by type Ⅱ and Ⅲ. The average kerogen vitrinite reflectance of the mudshale is more than 1 percent and can be as high as 3 percent or more. It is not difficult to find that the mudshale of Carboniferous-Permian in central Hunan has superior formation conditions of shale gas.The XRD analysis results indicated that the contents of brittle mineral in Carboniferous-Permian mudshale in the study area are higher than 50 percent on average, and the average value in the Upper Permian Dalong Formation mudshale can be as high as 79.8 percent. Test results of Ultrapore-200A helium porosimeter showed that porosity of mudshale is ranged from 0.2 percent to 14.9 percent, with an average value being 3.7 percent. Test results of Ultra-permTM200 permeameter showed that permeability of mudshale is ranged from 0.003 milidarcy to 0.07 milidarcy, with an average value being 0.015 milidarcy. It is not hard to find that Carboniferous-Permian mudshale in central Hunan has poor physical property, and strong reservoir heterogeneity.By using the probability volume method, the shale gas resources of Carboniferous-Permian in central Hunan is 2.8 trillions cubic meters. Among them, the shale gas resources (1.2 trillions cubic meters) and resource abundance (0.102 billions cubic meters per square kilometers)in Lower Carboniferous Ceshui Formation is biggest, followed by the Upper Permian Longtan Formation, with the values being 0.98 trillions cubic meters and 0.072 billions cubic meters per square kilometers, respectively. The shale gas resources and resource abundance in Upper Permian Dalong Formation is lowest, with the values being 0.62 trillions cubic meters and 0.06 billions cubic meters per square kilometers, respectively.By the method of comprehensive information superimposition, Lianyuan-Loudi, Lengshuijiang-Xinhua and Longhui-Xinshao are optimized as the favorable areas of shale gas exploration and development in Lower Carboniferous Ceshui Formation, and Lianyuan-Loudi, Lengshuijiang and Dengjiapu-Sanbitian are optimized as the favorable areas of shale gas exploration and development in Upper Permian Longtan Formation. In addition, Qixingjie of Lianyuan is optimized as the favorable areas of shale gas exploration and development in Upper Permian Dalong Formation.